No abstract available

[en] In the research project 'Determination of steel structures by means of ultrasound' methods are developed for the non-destructive structure characterization with scattered ultrasound. Measurements were made at about 200 steel samples with frequencies between 5 and 20 Mc/sec. In the range of 0,05 <= d/lambda <= 0,5 (d=mean grain size, lambda = wavelength of the ultrasound pulse) known theories can be applied for the quantitative grain size determination and with an accuracy of +-15% the results agree with the metallographically measured values. The best method for this is the combination of two measurements with two different frequencies. Advantages are given by the measurement of the multiple scattering which is leading to the scattering coefficient and to the grain size with one measurement only and without assumptions concerning other parameters of ultrasound propagation. A structure characterization concerning the homogeneity inside the material is possible, too, because of the time (i.e. sound path-)-dependent scattering measurement. It is able to control the structure of monophasic steels with grain sizes between ASTM 1 and ASTM 11. Today problems unsolved are the martensitic steels, the multiphasic structures

[en] In this work, high temperature solid phase method was applied to prepare Sr₂MgSi₂O₇:Eu, Dy blue light long-persistence materials with different contents of H₃BO₃. Under the condition of low H₃BO₃ content, it was difficult for Eu and Dy to enter Sr₂MgSi₂O₇ lattice, impurity phase of Sr₃MgSi₂O₈ was observed, and initial afterglow luminance of the sample was very low. With the increase of H₃BO₃, Sr₃MgSi₂O₈ phase disappeared, Eu and Dy entered Sr₂MgSi₂O₇ lattice smoothly, and the grain size as well as initial afterglow luminance of samples increased significantly. The initial afterglow luminance of the sample reached the maximum while the H₃BO₃ content was 10% (molar ratio). As H₃BO₃ content increased further, the initial afterglow luminance reduced rapidly. After detailed analysis, we consider that the key factors influencing the afterglow luminance of samples are the formation and the density of luminous unit, which is greatly determined by the Eu and Dy’s entering Sr₂MgSi₂O₇ lattice as well as the grain size of Sr₂MgSi₂O₇ crystal. (paper)

[en] Commercial copper was submitted to a thermomechanical treatment in order to study its influence on the velocity of artificial green patina formation by immersion as well as on the thickness and adherence of the corrosion product formed on the underlying metal. The thermomechanical treatment enabled us to obtain samples with 9 to 60 μm grain size. The samples were submitted to an accelerated attack by immersion in an electrolytic bath in order to obtain a green patina. On the smallest grain size material it can be observed a patina with high thickness and adherence smooth texture and homogeneous morphology. From the electrochemical assays it was established that the passivity current decreases for decreasing grain sizes. These results are consistent with the minimal porosity presented by the patina morphology which increase the protecting power. The underlying material did not present localized attack. (Author) 10 refs

[en] In a can resistant to stress crack corrosion, made of a zirconium alloy, the geometric mean value of the grain diameter of the zirconium alloy is less than or equal to 3 μm. This can is simply and cheaply made from an initial tube, which is rolled without recrystallisation annealing and free of cracks, so that there is a change of crossection of the pipe wall in the range of 90% or more. (orig.)

[en] (1 − x)Bi_0.5Na_0.5TiO₃−xBa_0.3Sr_0.7TiO₃ (abbreviated as BNT-BST, x = 0.05 ~ 0.40) was prepared by a conventional ceramic processing method and their structural evolution, dielectric and ferroelectric properties were investigated. The structure of the BNT-BST ceramics changes from phase coexistences of Rhombohedral-Tetragonal (x ≤ 0.10) to Tetragonal-Cubic (x ≥ 0.35), across a dominant Tetragonal phase region (0.15 ≤ x ≤ 0.30). By increasing BST content, the grain size of the BNT-BST ceramics slightly decreases, while the temperature T_m of the maximum dielectric constant gradually goes downward from ~ 250 °C to near room temperature. Meanwhile, with the increase of measuring frequency, the T_m increases for the BNT-BST ceramics with x ≥ 0.15, indicating their relaxor ferroelectric characteristics. Room temperature P-E loop test results show that both coercive field E_c and remnant polarization P_r gradually reduce with the increase of x value for relaxor BNT-BST ceramics. Both high peak dielectric constant (ε_r > 6000 at T_m) and saturated polarization (P_s ~ 30 µC/cm²), as well as tunable remnant polarization P_r are obtained in relaxor BNT-BST ceramics suitable for capacitor candidate materials.

[en] The effects of grain sizes and sensitization on the creep behavior of AISI 304 stainless steel was investigated. The study state creep rate of sensitized specimens was always larger than that of non-sensitized ones. The carbides were precipitated on grain boundary during creep and this seemed to have an effect on steady-state creep rate. All of ruptured specimens mainly showed intergranular cracking. (Author)

[en] Microstructure evolution in non-conserved and volume-conserved isotropic two-phase grain structures, with equal interfacial energy for all interfaces and equal volume fractions of the two-phases, is compared based on large-scale phase-field simulations. Two important observations are as follows: (1) the growth mechanism has a larger effect on the grain size distributions of the two alloys than on their grain topology distributions; (2) the growth rate and normalized grain size relation of the grains per topological class are much more scattered for the conserved system than the non-conserved system.

No abstract available

[en] In the present research, the surface-melted aluminum bronze were manufactured by laser remelting technology. The microstructure and properties of the melted layers with and without using activator were investigated. With increasing laser power, the width and depth of the melted layer increased, and the grain size of the melted layer became coarser due to the higher heat input and larger molten pool volume. Under the same conditions (i.e. laser power of 1000 W), the width and depth of the melted layer could be reduced and increased, respectively, with the use of the activator. In particular, the depth of melted layer increased by nearly 50%. Furthermore, to obtain the same penetration of the melted layer, the addition of the activator could reduce the heat input, which led to the decrease of grain size. The relatively small grain size and high dislocation density could improve the hardness and tribological behavior of the melted layers. (paper)